1. Field of the Invention
The present invention relates to a field emission display device fabrication method, and particularly to an improved field emission display device fabrication method of fabricating an improved field emission display device in a silicon wafer direct bonding method and a mold method.
2. Description of the Conventional Art
Generally, a field emission display device fabrication method is classified into a metal tip vacuum evaporation method of C. A. Spindt which is directed to using a pin hole mask and a silicon tip method of H. F. Gray, which is directed to forming layers by a silicon etching.
In addition, the field emission display device fabrication method is classified into a method of using a metal tip and a method of using a silicon tip in accordance with the tip material used so as to fabricate the field emission display device. In this case, each has its inherent disadvantage.
That is, the method of using a metal tip as a field emission display device material has an advantage in that it has good physical and chemical durabilities as well as has a relatively high field emitting current density; however, it is somehow difficult to precisely control fabrication conditions such as a precise diameter at one end of the tip and the height of the tip. In addition, the method of using a silicon tip as a field emission display device material has an advantage in that it can prevent a thermal mismatch because the tip and the substrate are made of the same material when forming a tip on a silicon substrate, the fabrication steps thereof are compatible to the existing VLSI steps, and desired configurations of the product can be achieved more easily; however, in this case, the physical and chemical durabilities of the product are weak compared with using a metal material, and it is difficult to achieve a desired field emitting current level.
In 1981, H. F. Gray et, al. introduced a mold technique so as to more easily fabricate a tip having a good uniformity and a geometrical characteristic. In addition, in 1990, M. Sokolich et al disclosed an improved field emission display device fabrication method of emitting an electron field at a lower current level of about 10V.
In addition, 1993 and 1994, M. Nakamoto et al. (Revue "Le Vide, les Couches Minces"--Supplement au N.sup.o 271-Mars-Pvril 1994, pp.41-44) introduced a transfer mold technique which is characterized to forming a field emission display device on a glass substrate, while performing a thin film deposition process and a photo etching process at the same time after transferring a tip array formed by the above-mentioned technique on a glass substrate.
Referring to FIGS. 1A through 1E, the above-mentioned conventional field emission display device fabrication methods will now be explained.
To begin with, the method of M. Sokolich et. al., (IEDM(International Electron Devices Meeting) Technical Digest, pp.159-162 (1990)) is directed to depositing an insulating layer on a silicon wafer 1, and patterning by a photo etching process so as to form an insulation film pattern 2 as shown in FIG. 1A.
Thereafter, as shown in FIG. 1B, a region of a silicon wafer of the insulation film pattern 2 is etched using a KOH aqueous solution in an orientation dependent etching method so as to form a pyramid-shaped hole 3 having a very sharp top.
In addition, as shown in FIG. 1C, a tip 4 is formed, and the silicon wafer 1 and the insulation film pattern 2 are removed to expose a tip 4 which is made of only the tip material.
Thereafter, as shown in FIG. 1D, a gate insulation film 5 and a gate electrode 6 are deposited on the tip 4 in order, and etched by a photo-etching process so as to form a field emission display device.
Next, the method of M. Nakamoto et. al. will now be explained. The method thereof has the same processes as the processes shown in FIGS. 1A through 1C. That is, the method of M. Nakamoto et al. is directed to transferring a tip from a silicon substrate to a glass substrate by bonding a top region of the tip 4 and a glass substrate 7 by an electrostatic thermal bonding method.
Here, the electrostatic thermal bonding method denotes bonding two materials using a high electron field formed on a boundary by applying a proper heat and a direct current voltage thereto after making a conjunction between a metal or a semiconductor and a glass.
Thereafter, the mold silicon substrate 1 is removed by a moisture etching, the gate insulation film 5 and the gate electrode 6 are formed on the tip 4 and patterned by a photo-etching process to form a field emission display device.
Next, the field emission display device fabricated in the method of M. Sokolich et al. is directed to using the substrate as a tip material formed by the deposition. In addition, the transfer mold technique is directed to forming a field emission display device on a glass substrate, thus achieving a more stable operation and a recommended standard environment.
As described above, when fabricating a field emission display device in the silicon mold method, it is possible to achieve the above-mentioned desired advantages.
That is, by varying the regional surface to be etched, it is possible to select a desired bottom surface of the tip, the height thereof, and in addition, various kinds of geometrical configurations can be obtained. Moreover, a reproducible field emission display array can be obtained, and a wide range of the tip material is available.